Conventional facsimile machines are mainly of the type that communicate monochrome information. In the communication of monochrome information, the receiving machine notifies the transmitting machine of its receivable resolution by way of a DIS (Digital Information Signal), and the transmitting machine instructs the receiving machine of the transmitted resolution and document width by way of a DCS (Digital Control Signal). This exchange of control information is performed in similar fashion also in the communication of color information as defined by current ITU-T recommendations.
Further, e.g., JP-A-7-177332 discloses that improving efficiency of facsimile transmission of which originals include a monochrome page and a color page by extending DIS and DCS specified in ITU-T Recommendation T.30 and by informing whether a color page is included in the originals being transmitted or not and information relating to receiving capability of a color original.
At the present time, facsimile machines that communicate color information use JPEG encoding stipulated by ITU-T Recommendation T.82 and execute the transmission of grayscale information and full-color information in Lab color space according to ITU-T Recommendation T.42.
Meanwhile, the rapid popularization of digital cameras in recent years has been accompanied by fast-growing demand for the facsimile transmission of color-file information (color-image information) for color images captured by such cameras. The color space used in a digital camera is sYCC (sRGB-based YCC) and not Lab.
Transmission of JPEG full-color document information in Lab color space in the prior art is strictly transmission of document information, namely information read by a reading unit, in a manner similar to a case where monochrome document information is transmitted as binary information, and therefore resolution and image-width information can be obtained and it is possible to specify resolution and image width in a DCS signal. On the other hand, in the case of JPEG full-color transmission in sYCC color space, there are many instances where the transmission is of image information captured by a digital camera and stored in, e.g., a memory card. However, the concept of resolution is absent from an image file (non-document image information), which is produced without the reading of a document as in the manner of an image file in sYCC color space captured by a digital camera. Consequently, in a case where such an image file is transmitted using the above-described control procedure, it is required that the image width and resolution information specified in the control procedure (DCS) be decided by the number of pixels in the main-scan direction and the number of pixels in the sub-scan direction. This necessitates the task of converting file information.